X-ray imaging is important in many technical fields including medical applications, baggage inspection, or material science.
Over the past several years, X-ray baggage inspections have evolved from simple X-ray imaging systems that were completely dependent on an interaction by an operator to more sophisticated automatic systems that can automatically recognize certain types of materials and trigger an alarm in the presence of dangerous materials. An inspection system has employed an X-ray radiation source for emitting X-rays which are transmitted through or scattered from the examined package to a detector.
It may be advantageous to calibrate an X-ray image apparatus to improve accuracy.
WO 2005/006257 A2 discloses an imaging system comprising artifact reduction means arranged to correct for a ring-shaped artifact in the three-dimensional reconstructed volume. The artifact reduction means comprises a first stage correction means arranged to eliminate the structured noise of the output screen of the image intensifier of an X-ray imaging apparatus using a first corrective image. The first corrective image may be pre-calculated and stored in a suitable memory unit of a computer. A raw image of the patient is first processed with the first corrective image. The thus obtained gain-corrected image is forwarded to an image deformation correction means, where a suitable unwarping function is being pre-stored. The resulting gain-corrected unwarped images are then made available to the second stage gain correction means, where a second corrective image is applied to the images resulting in a final set of images with a substantially reduced ring-shaped artifact. The final set of images is made available to the image reconstruction means arranged for further processing of the final set of images, the result thereof being visualized on a computer monitor for inspection purposes.
However, the system of WO 2005/00657 A2 may suffer from insufficient gain correction capabilities under undesired circumstances.